Wireless communication systems provide for radio communication links to be arranged within the system between a plurality of user terminals. Such user terminals may be mobile and may therefore be known as mobile stations.' At least one other terminal, e.g. used in conjunction with mobile stations, may be a fixed terminal, e.g. a control terminal, base station, or access point. Such a system typically includes a system infrastructure which generally includes a network of various fixed installations such as base stations, which are in direct radio communication with the mobile stations. Each of the base stations operating in the system may have one or more transceivers which may, for example, serve mobile stations in a given local region or area, known as a ‘cell’ or ‘site’, by radio frequency (RF) communication. The mobile stations which are in direct communication with a particular base station are said to be served by the base station, and all radio communications to and from each mobile station within the system are made via respective serving base stations. Sites of neighbouring base stations in a wireless communication system may be offset from one another or may be overlapping.
Wireless communication systems may operate according to an industry standard land mobile radio (LMR) protocol such as, for example, the Project 25 (P25) standard defined by the Association of Public Safety Communications Officials International (APCO), the Digital Mobile Radio (DMR) standard, or other radio protocols. Communications in accordance with DMR, P25, or other standards may take place over physical channels in accordance with one or more of a TDMA (time division multiple access) protocol, a FDMA (frequency divisional multiple access), or CDMA (code division multiple access) protocol. Mobile stations in wireless communication systems such as DMR systems send and receive user communicated voice data (e.g., voice or audio alone or multiplexed with other data such as video or image data) and non-voice data (e.g., location data or sensor data, control signalling, etc.), herein referred to collectively as ‘traffic information’, in accordance with the designated protocol.
Furthermore, LMR systems may operate in either a conventional or trunked configuration. In either configuration, a plurality of mobile stations may be partitioned into separate groups of mobile stations, such that mobile stations may selectively participate in individual (mobile station to mobile station) calls and also in group (mobile station to many mobile stations) calls.
In a conventional system, each mobile station in a group is selected to a particular FDMA frequency for communications associated with that mobile station's group. Thus, each group is served by one frequency (e.g., channel), and multiple groups may share the same single frequency (in which case, in some embodiments, group IDs may be present in the group data to distinguish between groups using the same shared frequency). In some systems, each conventional frequency may be further configured to carry multiple channels via a TDMA protocol, which allows for multiple concurrent calls on each frequency based on the configured ratio of the TDMA channels.
In contrast, a trunked radio system and its mobile stations use a pool of traffic channels (e.g., FDMA or TDMA protocols operating on a plurality of available physical frequencies) for virtually an unlimited number of groups of mobile stations (e.g., talkgroups). Thus, all groups are served by all channels. The trunked radio system works to take advantage of the probability that not all groups need a traffic channel for communication at the same time. When a member of a group requests a call on a control or rest channel on which all of the mobile stations in the system idle awaiting new call notifications, in one embodiment, a call controller assigns a separate traffic channel for the requested group call, and all group members move from the assigned control or rest channel to the assigned traffic channel for the group call. In another embodiment, when a member of a group requests a call on a control or rest channel, the call controller may convert the control or rest channel on which the mobile stations were idling to a traffic channel for the call, and instruct all mobile stations that are not participating in the new call to move to a newly assigned control or rest channel selected from the pool of available channels. With a given number of channels, a much greater number of groups can be accommodated in a trunked system as compared with conventional radio systems.
Group members for group calls conducted on conventional or trunked systems may be statically or dynamically defined. That is, in a first example, a user or administrator working on behalf of the user may indicate to the switching and/or radio network (perhaps at a call controller, push-to-talk (PTT) server, zone controller, or mobile management entity (MME), base station controller (BSC), mobile switching center (MSC), site controller, Push-to-Talk controller, or other network device) a list of participants of a group at the time of the call or in advance of the call. The group members (e.g., mobile stations) could be provisioned in the network by the user or an agent, and then provided some form of group identity, identifier, or address, for example. Then, at a future time, an originating user in a group may cause some signalling to be transmitted indicating that he or she wishes to establish a communication session (e.g., group call) with each of the pre-designated participants in the defined group. In another example, mobile stations may dynamically affiliate with a group (and also disassociate with the group) perhaps based on user input, and the switching and/or radio network may track group membership and route new group calls according to the current group membership.
Many wireless communication systems, including many LMR systems, provide for non-voice data transmission capabilities on a same traffic channel as voice communications or on one or more separate data revert channels. Data transmission capabilities may be used to periodically or semi-periodically (e.g., intermittently) report location information of mobile stations, determined via a GPS system, triangulation process, or some other method, or to periodically or semi-periodically report other types of data such as sensor information. Reported sensor information may include environmental conditions surrounding the mobile station, or health conditions (e.g., pulse rate, temperature, oxygen level, breath rate, etc.) of the mobile station's user, among many other possibilities. Such location and sensor information is usually short in nature (e.g., does not require a large amount of bandwidth to transmit, and can normally be transmitted in under one second), but is reported in a periodic or semi-periodic manner so that infrastructure applications, devices, and/or dispatchers can be provided with updated information over time. Other types of periodic and semi-periodic information may be transmitted as well.
As the number of applications that utilize or depend upon such periodic or semi-periodic data transmissions grow, the amount and frequency of such transmissions has grown as well. One problem that has arisen with respect to the periodic or semi-periodic transmission of non-voice data from mobile stations during group or individual calls is that calls having an excessive duration impair the ability of any one particular mobile station participating in the call from reporting such periodic or semi-periodic data. In other words, while a particular mobile station is participating in voice activity (e.g., transmitting and/or receiving voice data to and/or from one or more other mobile stations) it is unable to transmit the periodic or semi-periodic non-voice data. As a result, applications, devices, and/or dispatchers in the infrastructure relying upon the transmissions are starved of data, which could lead to negative consequences, especially in first responder wireless communications systems. One solution to the problem may be to provide a second transceiver in each mobile station and a second dedicated wireless channel on which to transmit such periodic or semi-periodic data. However, implementing a second transceiver and associated additional wireless channels substantially increases costs associated with implementing the supporting wireless communications system.
Accordingly, what is needed is an improved method, device, and system for transmitting short data in a wireless communication system.